Volatile organic compound (VOC's) present in the groundwater and subsurface at superfund sites are of concern because of their known potential to produce adverse health effects. Specific Aim 1 will determine the acceptability of scaling pressure- saturation relationships when expansive clay is present in the soil. Scaling parameters obtained from pressure- saturation measurements and those obtained from surface tension measurement will be used to determine the validity of the method and indicate the applicability of multiphase flow models employing scaling. These models are important for assessing the movement of chemicals near dump sites. Specific Aim 2 will investigate the influence that Boyd's (Project 2) organo modification of the clay content of a soil has on the hydraulic characteristics of the soil. Measurements will include NAPL and water- saturated intrinsic permeability and pressure-saturation relationships for the three pair of two-phase systems (air-water, air-NAPL, and NAPL-water). The measurements will be for one soil before and after the treatment that modifies the clay to produce the organoclay. This understanding is essential in order to employ modified organoclay soils in remediation efforts at waste dumps. Specific Aim 3 will develop a numerical solution for one-dimensional VOC transport in unsaturated soil using an expanded form of the preferential flow path model of van Genuchten and Wierenga. Further modification to account for chemical partitioning into the air phase will be made so that the model can be used to simulate VOC transport in unsaturated soil. Specific Aim 4 will determine the validity of the numerical model and the individual influence of the different transport mechanisms over a range of saturations by conducting a series of column experiments. Breakthrough tests on soil columns with three tracers of differing character will be used to obtain relatively independent information on the different processes.